On Wed, Oct 2, 2013 at 3:45 PM, Jan Hubicka <hubi...@ucw.cz> wrote: >> So I thing we ought to honnor accumulate-outgoing-args again and in fact >> consider disabling it for generic - it is disabled for core (that may need >> re-benchmarking). For all AMD targets it is currently on. I tested disabling >> it on buldozer 32bit and it seems mostly SPEC neutral for specint2000 (I am >> wating for more benchmarks) with very nice code size improvements in all >> benchmarks with exception of MCF with LTO (not sure at all why), with overall >> reduction of 5.2% (same gain as we get for -flto aproximately) >> http://gcc.opensuse.org/SPEC/CINT/sb-megrez-head-64-32o-32bit/size.html > Specint 2000/2006 seems quite good. (though for spec2k6 the differences in > sizes > are no longer anywhere near to -flto code size reductions) > > Unfortunately there is 40% regression on mgrid with -flto (and also noticeable > regression without LTO). First thing I noticed is that we stop omitting frame > pointer in the hottest function. This is because we see:
Does it happen with both 32-bit and 64-bit? > (set (reg/f:SI 7 sp) > (plus:SI (reg/f:SI 7 sp) > (const_int -8 [0xfffffffffffffff8]))) > > and we end up marking SP as as uneliminable in: > > /* See if this is setting the replacement hard register for > an elimination. > > If DEST is the hard frame pointer, we do nothing because > we assume that all assignments to the frame pointer are > for non-local gotos and are being done at a time when > they are valid and do not disturb anything else. Some > machines want to eliminate a fake argument pointer (or > even a fake frame pointer) with either the real frame > pointer or the stack pointer. Assignments to the hard > frame pointer must not prevent this elimination. */ > > for (ep = reg_eliminate; > ep < ®_eliminate[NUM_ELIMINABLE_REGS]; > ep++) > if (ep->to_rtx == SET_DEST (x) > && SET_DEST (x) != hard_frame_pointer_rtx > && (! (SUPPORTS_STACK_ALIGNMENT && stack_realign_fp > && REGNO (ep->to_rtx) == STACK_POINTER_REGNUM) > || GET_CODE (SET_SRC (x)) != PLUS > || XEXP (SET_SRC (x), 0) != SET_DEST (x) > || ! CONST_INT_P (XEXP (SET_SRC (x), 1)))) > setup_can_eliminate (ep, false); > > It is because of > > && (! (SUPPORTS_STACK_ALIGNMENT && stack_realign_fp > && REGNO (ep->to_rtx) == STACK_POINTER_REGNUM) > > I am somewhat confused why do we need to stop eliminating. Function is not > marked as needing drap (and in that case stack_realign_fp would be true) > What is this conditional shooting for? Why is stack_realign_fp true? -- H.J.
